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The studies were performed with 100 mg/L of Reactive Black 5 dye (RB5) in batch reactors on Ti/PtOx–RuO2–SnO2–Sb2O5 electrodes prepared indigenously. The electrodes were fabricated using titanium substrate (plate) and coated with mixed metals of a fixed composition by standard thermal decomposition (STD) and polymeric precursor thermal decomposition (PPTD) methods. The electrolysis up to 1 h was accomplished at a constant current density of 50 mA/cm2. For the process, an initial pH of 2 was maintained with the dosage of 4 g/L NaCl as supporting electrolyte. The effects of electrodes on colour, chemical oxygen demand, and total organic carbon removal were investigated for destruction of RB5. In this comparative study, while complete decolourizations of water containing RB5 were achieved on the electrodes prepared by STD and PPTD methods, but COD and TOC removal was found to be different for different electrodes at operating conditions. The 87% COD and 83% TOC removals were achieved on Ti/PtOx–RuO2–SnO2–Sb2O5 electrode prepared by PPTD method, in comparison to 83% COD and 80% TOC removals on the electrode prepared by STD method. The two types of electrodes were compared based on removal rate constant, mass transfer coefficient, instantaneous current efficiency, energy consumption, and accelerated life test. The energy demand for RB5 removal in this study was less than 250 kWh/kg COD, which is much lower than the reported values in similar studies. Further, the performance of electrodes was compared employing scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analysis for coating deposited on Ti substrate, and also by cyclic voltammetry. [ABSTRACT FROM AUTHOR]

The processing of liquid steel uses a very high temperature. The reaction between the liquid steel and the slag generates liquid-liquid mass transfer of the species involved. The mass transfer coefficients of the metals present in the stainless steel crude alloy were the central point of this study. The study in particular aimed to estimate the liquid-liquid mass transport coefficients of the species involved in this very important process. These were evaluated using the experimental results obtained from direct smelting of mixed low-grade chromite and nickel laterite ores. In this investigation, the kinetics of slag-metal reactions was stimulated by metal phase control mechanism and slag phase control mechanism. Results obtained from the experiments showed that the metal phase control was the dominating mechanism in the study as seen from the degree of fit of the experimental data to such mechanism. [ABSTRACT FROM AUTHOR]

Over the past decade, drug carries of various kinds have been used in the field of drug release control operations. It is agreed that drug carries maintain the concentration of drugs within the required range for a long period of time and reduce the toxicity resulting from the use of overdoses and the ability to direct the drug to the affected area. In this research activated carbon was used as an organic carrier in two different sizes (0.6 μm size with surface area 544.4704 m2/g and 11.042 nm size with surface area 985.6013m2/g ) and cefixime was used as a drug model ,The loading process was based on the adsorption between the surfaces of activated carbon molecules and the drug molecules dissolved in ethanol. The maximum efficiency of the experiments was 73% when the carbon in nanoparticle size and the carrier-to-drug ratio weight were 1.5, The unloading process was studied by studying the mass transfer coefficient and knowing the effect of the variables on its value ,these variables are time and temperature in addition to the PH value of the solution. The highest value of the mass transfer coefficient was obtained at the beginning of the unloading time ,at temperature 37 co and at PH 1.5 for dissolution medium .added to it proved that when using nanoparticle sizes, the unloaded (release) of the drug is more controlled over time than if the size of the carbon particles and the latter are better than if the drug is pure. [ABSTRACT FROM AUTHOR]

In this study, the effects of medium carbon chain alcohol (1-heptanol)-enhanced air sparging (AS) on the remediation of benzene-contaminated aquifers in different media (medium sand, channelized flow; gravel, bubbly flow) were investigated by comparison with a commonly used surfactant (sodium dodecylbenzene sulfonate (SDBS)). The results showed that the addition of 1-heptanol and SDBS significantly increased the air saturation in AS process under different airflow modes. Combined with water retention curves, 1-heptanol had the same effect on reducing the surface tension of groundwater and stabilizing bubbles as SDBS. In the study of benzene pollution removal, when the removal efficiency of the benzene pollutant exceeded 95%, the time required for surfactant-enhanced AS (SEAS) and alcohol-enhanced AS (AEAS) in medium sand was shortened by 28.6% and 52.4%, respectively, and the time required for SEAS and AEAS in gravel media was shortened by 16.7% and 58.3%, respectively, compared with the time required for AS. This finding indicated that the addition of SDBS or 1-heptanol could significantly increase the removal rate of benzene pollutants. Under the same surface tension conditions, the removal effect of 1-heptanol on the benzene pollutant was better than that of SDBS. This difference was due to the disturbance of the flow field during AEAS process causing the 1-heptanol on the gas-liquid interface to volatilize in the carrying gas, thereby inducing Marangoni convection on the interface, enhancing the gas-liquid mass transfer rate, and increasing the removal rate of benzene on the interface. Therefore, 1-heptanol is promising as a new reagent to enhance AS to remediate groundwater pollution. [ABSTRACT FROM AUTHOR]

• Artificial neural network was employed as an approach to predict K L a for ozone absorption in RPB. • Serial experiments were conducted to obtain data for modeling. • Random grid research was applied for hyperparameter tuning in artificial neural network. • The obtained model had a satisfactory performance of 0.9896 R2 on the training set and 0.9877 R2 on the test set. It has been proved that Higee technology can intensify the processes involving the multiphase mass transfer, and be applied to the ozone-based advanced oxidation processes. Modeling and prediction of mass transfer coefficient are rare in this field. A modeling approach based on artificial neural network (ANN) was developed in this work to predict mass transfer coefficient of ozone absorption process in rotating packed bed (RPB). Serial experiments were conducted to obtain data for the establishment of ANN model, which was then employed to predict the overall mass transfer coefficient (K L a) using dimensionless quantities such as Reynolds number of gas and liquid, Froude number and Weber number, calculated in terms of the geometry of RPB and operating conditions. To optimize the model structure and performance, random grid search for hyperparameters was adopted in this work. The final model exhibits a prediction ability with R2 of 0.9896 and 0.9877, RMSE of 0.01801 and 0.03085, and MAE of 0.01265 and 0.02219 on the training set and the test set, respectively. [ABSTRACT FROM AUTHOR]

The effects of cellulose, surfactants, and their combination on the hydrodynamic behavior and the liquid‐side mass transfer coefficient of a bubble column were evaluated. For that purpose, different aqueous solutions containing surfactants (sodium dodecyl sulfate) and cellulose (microcrystalline cellulose, MCC) were investigated. The interfacial areas were calculated from the bubble diameters, the bubble frequencies, and the terminal bubble rising velocities. The liquid‐side mass transfer coefficients were determined from the volumetric mass transfer coefficients measured by the dynamic method. In the concentration range under test, the experimental results proved that the addition of MCC to the studied liquid phases did not affect the mass transfer coefficient. [ABSTRACT FROM AUTHOR]

Vortex contact devices for gas introduction have been developed and studied. The devices make it possible to increase the gas and liquid loading on stages compared with valve and cap devices, to reduce the fluctuations of the gas–liquid medium on the liquid surface, and to increase the separation efficiency. Based on the experimental studies and numerical modeling, a scheme of liquid and gas motion at the stage was developed, and the velocity profiles during bubbling were calculated. The stage parameters were determined: hydraulic resistance, gas content, average surface diameter of bubbles, interphase surface area, efficiency, and mass transfer coefficients. The dependences for their calculation were presented. A vortex stage for the exhausting distillation column was designed, which provides a 1.5-fold reduction of metal consumption and increased efficiency at a velocity factor of up to 3 Pa0.5 and spray rate of 78 m3/(h m2) compared with the standard cap plate. [ABSTRACT FROM AUTHOR]

Physiochemical similarities of volatile compounds and their interactions with the beer matrix are the main challenging factors in selective separation of ethanol for the production of non-alcoholic beer and removal of excess (off-)flavours produced during fermentation, such as isoamyl acetate. In this paper, we are especially interested in the effect of beer dry matter, a complex mixture of carbohydrates and proteins, and of ethanol on flavour behaviour during treatment with a packed bed column using CO2 as a stripping agent. By analysing the gas phase at different dry matter concentrations, we observed that its’ presence is a facilitating factor for ethyl acetate and isoamyl acetate release, whereas isoamyl alcohol is retained in the liquid phase. These effects are a result of combined mass transfer effects and affinity for carbon dioxide, which are both affected by the presence of ethanol in the feed stream. Mass transfer analysis of isoamyl alcohol and ethanol revealed that the resistance is not controlled by their solubility in water but the affinity to C02. [ABSTRACT FROM AUTHOR]

Interphase mass transfer or dissolution coefficient of nonaqueous phase liquids (NAPL) is an important parameter in predicting the transport of contaminant species in porous media. While the literature offers valuable insights into the dependence of this coefficient on different parameters at the continuum scale (e.g., contaminant saturation and Darcy velocity), effects of pore‐scale heterogeneity on macroscopic dissolution coefficient have received little attention. In this work a three‐dimensional pore‐scale model is developed to simulate interphase mass transfer over different synthetic pore network structures with various pore radii correlation lengths. The pore network modeling simulates dissolution of immobile NAPL into water (single phase) through diffusive throats for the water‐NAPL interface. The impacts of pore network spatially correlated heterogeneities, NAPL saturation/distribution, and aqueous phase velocity on NAPL mass transfer coefficient and water‐NAPL interfacial surface area are studied. These macroscopic properties are then employed in two‐dimensional continuum‐scale domains formed by concatenating 20 by 20 pore networks in x and y directions. The results highlight the impact of pore‐scale heterogeneity on the distribution of NAPL and subsequently on the dissolution rate (i.e., dissolution coefficient). An uncorrelated distribution of pore radii consistently leads to higher NAPL dissolution coefficient than spatially correlated heterogeneity. The results of continuum modeling show that NAPL dissolution rates are only different between domains formed by correlated and uncorrelated pore networks at very high flow rates and Darcy velocities. However, for typical values of Darcy velocity in groundwater systems, variation in mass transfer coefficient due to pore‐scale heterogeneity is minimal for efficient mass removal. Key Points: Pore‐scale heterogeneity in the form of spatial correlation between pore radii is considered for NAPL dissolution into waterPore networks with spatial correlation led to lower mass transfer coefficients than those with randomly distributed pore radiiAt Darcy (cm) scale, effects of underlying pore‐scale heterogeneity on NAPL recovery can only be realized at high flow rates and at low NAPL saturations [ABSTRACT FROM AUTHOR]

Summary: An analytical model for contaminant transport in multilayered capped contaminated sediments including the degradation of organic contaminant is presented. The effect of benthic boundary layer was treated as a Robin‐type boundary condition. The results of the proposed analytical model agree well with experimental data. The biodegradation of contaminant in bioturbation layer shows a significant influence on the flux at the surface of system. The maximum flux for the case with t1/2,bio = 0.07 year can be 4.5 times less than that of the case without considering the effect of biodegradation. The thickness of bioturbation layer has a significant effect on the performance of the capped contaminated sediment. The maximum flux for the case with lbio = 15 cm can be 17 times larger than that of the case without bioturbation layer. This may be because the effective diffusion coefficient of sand cap can be 28 times lower than Dbio. The mass transfer coefficient should be considered for the design of the capping system as the contaminant concentration at the top of system for the case with kbl = 2.5 × 10−5 cm/s can be 13 times greater than that of the case with kbl = 10−4 cm/s. The proposed analytical model can be used for verification of complicated numerical methods, evaluation of experimental data, and design of the capping contaminated sediment systems with reactive cap layers. [ABSTRACT FROM AUTHOR]

• The effects of bubble behaviors on CO 2 absorption characteristics in nanoabsorbents are investigated. • The VOF method is selected to capture the coalescence and breakup processes of rising CO 2 bubbles. • Five types of bubble wakes and their effects on the bubble behaviors such as the coalescence and breakup are categorized. • A higher concentration of nanoparticles is favorable to CO 2 bubble coalescence and breakup. • The coalescence and breakup processes enhance the mass transfer performance by increasing the interfacial area. The objectives of this study are to present a comprehensive analysis of the CO 2 bubble population dynamics and to investigate their effects on the CO 2 absorption characteristics in nanoabsorbents (methanol with various concentrations of Al 2 O 3 nanoparticles) with a rectangular bubble column. The population balance model (PBM) as a well-established method based on the Euler-Euler model is employed to compute the size distribution of bubbles and to account for the bubbles coalescence and breakage in multiphase flow. The coupled volume-of-fluid (VOF) method is selected to clearly capture the coalescence and breakup processes of successively rising bubbles. The results show that there is a significant influence of the leading bubble on the following one, including the increment of the velocity, the deformation of the bubble shape and the flow instability. It is also found that the critical distance at which the influences can be exerted is related to the bubble wake trailed by the leading bubble. Accordingly, five types of bubble wakes and their effects on the bubble behaviors such as the coalescence and breakup are categorized. Finally, by further analyzing the bubble behaviors in methanol with different volume fraction of Al 2 O 3 , it is found that the coalescence and breakup of bubbles are dominated by the bubble wake and enhanced by the eddy in local liquid. It is concluded that the higher concentration of nanoparticles is favorable to the bubble coalescence and breakup, which enhance the mass transfer performance by increasing the interfacial area. [ABSTRACT FROM AUTHOR]

An accelerated erosion test with improved experimental efficiency is required to study the critical properties of pipe erosion failure in a reactor effluent air cooler used for the hydrocracking process. In this study, a single 90° elbow was simulated numerically with the design of an L16 orthogonal table to discuss the influencing factors of grid refinement at the bend. An analysis of the length–diameter ratio L1/D revealed that when L1/D increases to more than 5, the change in wall shear stress at the inner bend wall is insignificant. The mass transfer coefficient of ferrous ion and the maximum shear stress τm were also utilized to describe the erosion rate, including electrochemical corrosion and hydrodynamics. The factor that influenced mass transfer coefficient most was inlet velocity. The regions with high mass transfer coefficient were located at R1 and R2, with R1 showing a higher risk of electrochemical corrosion than R2. Operating pressure played a critical role in the effect on τm, which presented a low inside/high outside trend. The region with high τm was located at R3, where a high breakage risk of erodent product films was observed. [ABSTRACT FROM AUTHOR]

To promote the heat and mass transfer during the hydrate formation process, an internal spiral‐grooved tube (ISGT) was proposed as the reaction tube in a large‐scale multi‐tube bubble column reactor with external slurry circulation. In order to investigate such multi‐component gas (natural gas)‐water‐surfactant systems during the hydrate formation process in the ISGT, based on the solute permeation model and Kolmogorov isotropic turbulence theory, a CFD method combined with the population balance model (PBM) was utilized to simulate gas‐liquid mass transfer coefficient. Then, the hydrate formation kinetics model in ISGT was modelled based on the model proposed by Kashchiev and Firoozabadi. The hydrate formation experiments were carried out in the multi‐tube bubble column reactor at six different pressure‐temperature‐circulating flow velocities of piston pump regimes to investigate the actual formation process of natural gas hydrate. The experimental results were then used to finetune the optimized parameters to facilitate accurate model predictions. [ABSTRACT FROM AUTHOR]

Solid-liquid extraction of paclitaxel from the biomass of Taxus chinensis was investigated in order to understand the effect of temperature, solvent concentration and stirring speed on the mechanism and kinetics of extraction. Paclitaxel concentration-time data were analyzed using a second-order kinetic model to determine the kinetic parameters. A diffusion model was utilized to determine diffusivity and mass transfer coefficient taking into account both washing and diffusion phases together. The effective diffusion coefficient (1.2814 × 10−13-5.9765 × 10−13 m2/s), mass transfer coefficient (1.0020 × 10−7-1.2598 × 10−7 m/s), and Biot number (3.927–8.959) increased with increasing temperature (298–318 K), methanol concentration (75–100%) and stirring speed (170–570 rpm), which indicated that the external resistance to mass transfer is negligible due to efficient mixing of solute and solvent. [ABSTRACT FROM AUTHOR]

• Combined persulfate (PS)-membrane distillation improves micropollutant (MP) removal. • MP properties governed their degradation by PS from secondary treated wastewater. • MP degradation by PS led to their consistent removal by MD membrane. • Effluent organic matter degradation by PS helped mitigate membrane fouling. • Final treated water was non-toxic as confirmed by bioluminescence toxicity assay. In this study, long-term performance of a persulfate (PS)-assisted direct contact membrane distillation (DCMD) process was examined for the treatment of secondary treated effluent spiked with a mixture of micropollutants including three pesticides and nine pharmaceuticals. A stand-alone DCMD ('control') was also operated under identical operating conditions for comparison. Depending on the micropollutant, the stand-alone DCMD achieved 86 to >99% removal. In comparison, removal by the PS-assisted DCMD was >99% for all investigated micropollutants. This was attributed to the fact that sulfate radicals (SO 4 – ) formed following the activation of PS at the DCMD operating temperature (i.e., 40 °C) achieved micropollutant-specific degradation, which reduced the accumulation of micropollutants in the feed. Chemical structures of the micropollutants governed their degradation by PS. Effective degradation (>90%) was achieved for micropollutants that contain strong electron-donating functional groups (EDGs) in their molecules (e.g., amitriptyline and trimethoprim). Micropollutants containing both strong electron-withdrawing functional groups (EWGs) and EDGs in their molecules were moderately degraded (60–80%). In addition to the micropollutants, activated PS significantly degraded total organic carbon (70%) and total nitrogen (40%) from the secondary treated wastewater. This helped to reduce the fouling layer on the membrane-surface in the PS-assisted DCMD system. PS-addition appears to slightly increase the toxicity of wastewater, but with effective retention of PS and degradation products, DCMD permeate (i.e. , treated effluent) was not toxic. This is the first study demonstrating the performance of the persulfate oxidation process in a continuous-flow membrane system for micropollutant removal and membrane fouling control. [ABSTRACT FROM AUTHOR]

• The viscosity effect on the performance of a membrane contactor was studied. • Sugar and glycerol were used as viscosifiers to 30 wt% MEA and 3.9 wt% NaOH. • K ov decreased with increasing concentration of viscosifier. • Viscous solutions may create an extra resistance on the membrane/liquid interface. The effect of liquid viscosity on the performance of a non-porous membrane contactor is important to study for a proper solvent selection and process design. In this work, the overall mass transfer coefficient for MEA- and NaOH-based solutions was studied using a string of discs contactor in the temperature range 28–64 °C and a thin composite membrane contactor at 40 °C. Also, viscosity, density and N 2 O solubility of the aqueous solutions were measured in the temperature range 30–70 °C. The solvent viscosity of MEA and NaOH solutions was artificially adjusted from 0.5 to 54.7 mPa s by addition of sugar and/or glycerol. The overall mass transfer coefficient was found to decrease with increasing amount of viscosifier and the decrease seemed to be independent of the solvent system. In the membrane contactor, the decrease in the overall mass transfer coefficient was attributed to the decreasing CO 2 solubility and CO 2 diffusion coefficient, but as these properties alone were not able to describe the experimental values, the reason was attributed also to the establishment of an additional resistance at the membrane/liquid interface. [ABSTRACT FROM AUTHOR]

Modified atmosphere packaging (MAP) is applied to extend the shelf life of fresh and minimally processed produce. Commonly used films, such as oriented polypropylene (OPP), are too impermeable to gases for successful MAP for products with moderate to high respiration rates, which has led to perforated systems. In order to design the perforation profile to ensure MAP targets for extended shelf life, it is necessary to evaluate which parameters affect the mass transfer through the perforations significantly. Perforations (270 μm, 450 μm and 750 μm diameter) were made in an OPP film under different temperatures and circulating air velocities, considering also different locations for the perforations. The results obtained showed that the perforation diameter is the most important parameter and can even be more significant than the total area of perforation (and therefore the number of perforations). Air velocity around the package and storage temperature were also relevant. Stacking during storage risks blocking perforations and therefore it is recommended to pierce trays on the sides in order to ensure better robustness. The package gas composition itself also affected mass transfer due to the interplay of oxygen flux with other gas fluxes, with particular relevance to the case of water vapour. [ABSTRACT FROM AUTHOR]

Gas-liquid mass transfer in wastewater treatment processes has received considerable attention over the last decades from both academia and industry. Indeed, improvements in modelling gas- liquid mass transfer can bring huge benefits in terms of reaction rates, plant energy expenditure, acid-base equilibria and greenhouse gas emissions. Despite these efforts, there is still no universally valid correlation between the design and operating parameters of a wastewater treatment plant and the gas-liquid mass transfer coefficients. That is why the current practice for oxygen mass transfer modelling is to apply overly simplified models, which come with multiple assumptions that are not valid for most applications. To deal with these complexities, correction factors were introduced over time. The most uncertain of them is the a-factor. To build fundamental gas-liquid mass transfer knowledge more advanced modelling paradigms have been applied more recently. Yet these come with a high level of complexity making them impractical for rapid process design and optimisation in an industrial setting. However, the knowledge gained from these more advanced models can help in improving the way the a-factor and thus gas-liquid mass transfer coefficient should be applied. That is why the presented work aims at clarifying the current state-of-the-art in gas-liquid mass transfer modelling of oxygen and other gases, but also to direct academic research efforts towards the needs of the industrial practitioners. [ABSTRACT FROM AUTHOR]

An experimental investigation on liquid-wall mass transfer at the internal wall of a coiled flow inverter is carried out. Computation of the mass transfer coefficient is made from measured limiting currents at point electrodes fixed flush with the inner surface of the coiled flow inverter. Variation of mass transfer coefficient with respect to liquid velocity is studied. The coiled flow inverter yielded an enhancement of 125% in mass transfer coefficient against the reported enhancement of 35% in heat transfer. The data were correlated using the least squares regression method and a correlation equation is obtained. [ABSTRACT FROM AUTHOR]

• The overall mass transfer coefficient was obtained for NO absorption. • Liquid flow rate had minor effect on the absorption process. • Increase of temperature reduced the NO absorption efficiency. • An empirical model for the prediction of NO absorption efficiency was proposed. An empirical model was developed for the prediction of the absorption efficiency of nitric oxide (NO) into ammoniacal cobalt (II) solution in terms of gas flow rate, liquid flow rate, and temperature. The model parameters were determined experimentally using a spraying tower with initial absorbent solution pH of 10.0–10.2 for temperatures in the range of 281.15–323.15 K. The reactions between Co2+ complexes and NO were found to be in the fast pseudo-first-order reaction regime. The correlation between the overall mass transfer coefficient and the gas and liquid flow rates was determined for NO absorption. The liquid flow rate (0.225 to 0.730 L/min) had negligible effect on the NO absorption efficiency for the conditions with excessive Co2+ complexes in the solution due to the fast reaction rates. Temperature showed detrimental effects on the NO absorption for conditions in this study. [ABSTRACT FROM AUTHOR]

• The overall catalytic combustion kinetics of H 2 in air is studied. • Experimental data in low Peclet number region is generated (Pe 1.4 - 14). • The mass transfer coefficients were estimated for different Re p (7–77). • A correlation is developed in terms of Sh , Re p and S c for H 2 -air system. • Contribution of individual resistances was estimated at different Re p (7–77). The overall kinetics of catalytic combustion of hydrogen in air is decided by the contribution of the different resistances offered in individual steps such as external diffusion, internal diffusion and surface reaction. To estimate the contribution of external mass transfer resistance, empirical correlations in terms of dimensionless numbers viz. , Sherwood number, particle Reynold's number, and Schmidt number are used in general. The Schmidt number for hydrogen in air is approximately 0.2 and most of the mass transfer correlations in packed bed reactors are valid for Schmidt number higher than 0.6, which corresponds to that of water vapour in the air. The external mass transfer correlations applicable for hydrogen-air system are scarce. In the present study, the external mass transfer effects were decoupled from internal diffusion and intrinsic reaction by conducting experiments with different particle Reynolds numbers in a packed bed batch reactor with complete recycle. Further, the system is theoretically modeled and the external film mass transfer coefficients were estimated at different particle Reynold's numbers using experimental data. Based on the experimental data, a new mass transfer correlation has been proposed to determine the gas film mass transfer coefficient of hydrogen in the air in packed bed reactors, in terms of conventional dimensionless numbers i.e., Sherwood number, Schmidt number, and particle Reynolds number. Further, the contribution of external mass transfer resistance on the overall reaction kinetics was also estimated. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Novel composite PSf/PTMSP hollow fiber membranes are fabricated. • Ethylene/ethane separation in membrane contactor with aqueous AgNO 3 is studied. • Highest ethylene overall permeance (83 GPU) at ethylene recovery of 44% is achieved. • Ethylene overall permeance decreases only by 24% during six months of MC operation. • Membrane and liquid phase resistances are significant and comparable. Abstract The novel highly permeable composite membranes with a thin selective layer made of poly(1-trimethylsilyl-1-propyne) (PTMSP) on polysulfone hollow fiber support were proposed for application in gas-liquid membrane contactor for ethylene/ethane separation. The effects of AgNO 3 concentration in aqueous absorbent and its velocity on the ethylene mass transfer coefficient were evaluated. High ethylene permeance (83 GPU) at ethylene recovery of 44% was achieved. Six months of membrane contactor operation revealed only 24% drop in the overall mass transfer coefficient. The contributions of membrane and liquid phase to the overall mass transfer resistance were estimated. The contributions were found to be comparable values. [ABSTRACT FROM AUTHOR]

Ammonia emissions from animal production systems are a concern due to their potential adverse effects on the environment. It is important for governments to adjust their policies to control ammonia emissions from animal production. To evaluate and quantify emission factors, process-based modelling is a cost-effective procedure, particularly due to the complex and diverse transfer chains. During the modelling process, ammonia mass transfer coefficient is one of the key parameters to be determined. However, inconsistencies are found in widely used expressions for mass transfer coefficients in ammonia volatilization models. This study used CFD simulations to derive the mass transfer coefficients above metal and concrete slatted floor in an experimental pig houses with 12 full-scale pig pens. Five ammonia mass transfer coefficient models were selected for comparison with the models derived from CFD simulations. It was noticed that the models derived from wind tunnel/flux chamber experiments usually predicted lower values of ammonia mass transfer coefficients compared to the models developed from full-scale measurements and/or numerical modelling. Care is needed to extrapolate the relationships developed under controlled laboratory conditions to the commercial barns. The results indicated also that the ammonia mass transfer coefficient relies heavily on the airflow patterns which could be affected by the ventilation systems, location of the inlet and outlets, internal partitions, floor types etc.. This makes it very difficult to present a universal ammonia mass transfer coefficient model for pig houses. • The relationship between NH 3 mass transfer coefficient and the ventilation rate developed. • Models of ammonia mass transfer coefficient under two fan locations proposed. • New models of NH 3 mass transfer coefficient are compared models in literature. [ABSTRACT FROM AUTHOR]

One of the limitations to the application of columns to solvent extraction in the minerals industry is their relative inefficiency in slow kinetic systems such as those used for the separation of copper. In order to overcome this, this work examines the performance of a new kinetic internal and compares it to standard column internals for both a fast and slow kinetic system. The mass transfer performance of a pilot scale pulsed solvent extraction column with Tenova Kinetics Internals (TKI) and standard disc and doughnut internals (DDI) are compared, including the effect of pulsation intensity, continuous and dispersed phase velocities using the H 2 SO 4 – Alamine® 336 system, a fast kinetic system, and CuSO 4 – LIX® 84 system, a slow kinetic system. The height of mass transfer unit (H oc) for the CuSO 4 – LIX 84 system increased with continuous and dispersed phase velocity and decreased with the increase of pulsation intensity. The H oc for TKI was lower than the DDI for the same operating conditions and the TKI reduced the impact of both phase velocities on mass transfer. TKI can maintain the mass transfer performance for the fast kinetics H 2 SO 4 -Alamine 336 system compared to standard disc and doughnut internals and improve mass transfer performance for slow kinetics CuSO 4 - LIX® 84 system. An empirical correlation to predict the height of mass transfer unit in both internals was developed with absolute relative errors of 28.0% and 19.2% for the H 2 SO 4 – Alamine 336 system and CuSO 4 – LIX 84 system, respectively. • Tenova kinetics internals (TKI) enhances mass transfer of slow kinetics system. • TKI maintains mass transfer of fast kinetics system. • Increase pulsation and phase velocities reduces the H oc in slow kinetics system. • A correlation was developed to predict the H oc of multiple systems and internals. [ABSTRACT FROM AUTHOR]

We investigated the characteristics and mechanism of microwave-assisted drying of amorphous paclitaxel for the removal of residual solvent, acetonitrile. The removal efficiency of residual acetonitrile increased with increasing drying temperature from 35 to 55°C. When the experimental data were applied to typical kinetic models, the Page model was determined to be the most suitable. Thermodynamic parameters revealed the spontaneous and endothermic nature of microwave-assisted drying. The effective diffusion coefficient of acetonitrile (0.865 × 10−8∼ 1.553 × 10−8 m2/s) and the convective mass transfer coefficient (2.138 × 10−7∼7.656 × 10−7 m/s) increased with increasing drying temperature. The small Biot number (0.001975∼ 0.003939) indicated that the process of mass transfer was externally controlled. [ABSTRACT FROM AUTHOR]

Highlights • Welding electrospun hollow fiber membrane is firstly applied in ammonia removal. • The effect of membrane thickness on selectivity was intensively investigated. • Self-made membrane with high flux and selectivity favors ammonia recovery. • Self-made membrane demonstrates its potential in membrane absorption application. Abstract Excessive ammonia nitrogen in wastewater seriously endangers ecological environment, so high-flux and selectivity membrane is urgently needed for ammonia removal using membrane absorption (MA). In this paper, a high-performance electrospun hollow fiber membrane was fabricated and solvent vapor welding treatment was adopted to enhance mechanical strength. The post-treatment membrane showed 103.8% higher in the Young's modulus than the pristine membrane. High mechanical strength, porosity and hydrophobicity of the membrane make it superior in mass transfer and selectivity. The effects of membrane thickness, pH and temperature of feed solution on experimental overall mass transfer coefficient (K OE) and selectivity coefficient (S NH3/H2O (g)) were intensively investigated to examine the membrane performance in MA application. The results show K OE is 1.35 * 10−5 m s−1 and S NH3/H2O (g) is 7.58 when pH is 11, which are higher than that of commercial membrane. Moreover, the selectivity can be improved greatly from 6.91 to 9.74 by increasing the thickness of the hollow fiber membrane from 55 ± 5 μm to 115 ± 5 μm. The welded electrospun hollow fiber membrane demonstrates great potential for ammonia removal in MA application. [ABSTRACT FROM AUTHOR]

Abstract Reverse micellar extraction (RME), a liquid-liquid based separation is a versatile tool for protein purification. A statistical approach was employed for the purification of recombinant glutaminase free anti-cancerous enzyme viz., l -asparaginase II to evaluate the effects of RME in current study. The cationic system (CTAB/iso-octane/hexanol/butanol) was used in RME to optimize both forward and backward protein extraction efficiency. By adapting Taguchi's orthogonal array (OA), maximum forward extraction efficiency (FEE) of 86.98% with 84.82% enzyme activity recovery and 1.04 times purification fold achieved with the optimized parameters. Under the optimal levels, the back extraction efficiency (BEE) was observed to be 96.97% with 93.07% enzyme activity recovery and 1.38 times purification fold. Further, mass transfer kinetic studies of RME indicated the mass transfer coefficients of forward and backward extraction to be 0.049 min−1 and 0.036 min−1 respectively. Highlights • Reverse micellar extraction (RME) a simple, economical and a promising tool employed for purification of recombinant extracellular l -asparaginase II from Bacillus subtilis with a forward extraction efficiency (FEE) and a backward extraction efficiency (BEE) of 86.98% and 96.97% respectively. • A cationic system (CTAB/iso-octane/hexanol/butanol) was used to purify the enzyme using Taguchi method. • The mass transfer coefficients for both the forward and backward extraction were determined. [ABSTRACT FROM AUTHOR]

• Drop size distribution in the investigated column is best followed by the log-normal distribution. • Mass transfer coefficient of the large droplets is larger than that of the small droplets. • Volumetric overall mass transfer coefficient of the small droplets is greater than that of the large droplets. • Pulsation intensity and interfacial tension are the most important factors on mass transfer coefficient. The objective of this work is to model the effect of drop forward-mixing on the mass transfer efficiency of a two phase countercurrent extraction process. Based on the flow mechanism and drop size distribution in extraction columns, a novel model with a simplified sequential algorithm is developed. Unlike the other models that use mean diameter of the dispersed phase droplets, this model accurately considered the effect of drop size distribution on mass transfer efficiency. On the base of this model the volumetric overall mass transfer coefficient has been investigated in a pilot plant of L-shape pulsed packed extraction column by using two liquid systems of toluene/acetone/water and butyl acetate/acetone/water. It is found that, although the mass transfer coefficient related to the large droplets is larger but the corresponding volumetric overall mass transfer coefficient is less than that related to the small droplets. Therefore, any factor that reduces the drop size can improve the efficiency of mass transfer. Furthermore, the effect of operational variables and physical properties including the dispersed and continuous phases flow rates, pulsation intensity and interfacial tension have been considered on mass transfer coefficients. It has been found out that the pulsation intensity and the continuous phase flow rate have seriously affected on mass transfer coefficient, however, the dispersed phase flow rate has a weaker effect. Finally, new correlations are proposed to accurately predict the mass transfer coefficient, axial mixing and drop size distribution. Good agreement between predictions and experiments was found for all operating conditions that were investigated. [ABSTRACT FROM AUTHOR]

NOx, a generic term for nitrogen oxides, is an air pollutant that can causes damage to the ozone layer, and produces greenhouse effects, acid rain and photochemical smog. It is mainly produced by diesel engine exhaust due to the reaction between nitrogen and oxygen, especially at elevated temperatures. NOx needs to be reduced from flue gas in order to fulfil environment regulations due to its hazardous nature. This study aims to remove NOx from air through absorption using a mixture of H2O2 and HNO3 solutions as an absorbent in the membrane contactors. In the experiment, the feed gas and the absorbent were flowed in the shell side and the lumen fibers, respectively. The flow rates of absorbent and feed gas, as well as the fiber number the membrane contactor, greatly influence the efficiency of NOx removal, mass transfer coefficients and fluxes. The highest values of NOx removal efficiency, mass transfer coefficient and flux achieved in the study were 47%, 8.7×10-5 cm.sec-1, and 3.1×10-5 mmole.cm-2.sec-1, respectively. [ABSTRACT FROM AUTHOR]

One of the main problems with tray rectification units is the kinetic studies of their mass transfer which are complicated due to the difficulties in the determination of the interphase boundary formed by the dispersion of the vapour phase in the liquid on the tray, the mass transfer coefficient, as well as the mixing of the liquid by its movement on the tray and the presence of impurities in the separated mixtures. Many efforts have been devoted to this problem in recent years. The present paper is a contribution in this field. The influence of the kinetic coefficients by rectification of the binary system methanol-water under complete mixing of the liquid phase and regime of ideal shift of the vapour phase was studied. To approximate these idealised models of the motion of the two phases, the experiments were carried out in a specially manufactured small scale laboratory column equipped with three sieve trays. [ABSTRACT FROM AUTHOR]

This paper deals with mathematical modeling and simulation of methanol carbonylation reactor in acetic acid production plant that consisted of a continuous stirred tank reactor (CSTR), a flash drum, a Joule-Thomson valve, and a condenser. The model was based on material and energy balances that considered liquid-gas mass transfer, thermodynamics, and reactor hydrodynamics. The most important aspect of the model was the selection of an appropriate correlation for prediction of mass transfer coefficient. Several correlations were examined and comparison of the model results with plant data indicated that the correlation reported by Lemoine was most appropriate. The simulation results were found to be in good agreement with plant data and the effects of various operating parameters on the performance of the model such as temperature of reactor from 186 °C to 183.6 °C, CH3I concentration from 3.11 mol% to 2.21 mol% and agitator rotation speed from 62 rpm to 112 rpm were investigated. [ABSTRACT FROM AUTHOR]

Highlights • The optimal molar ratio of DMEA/MEA solution with low heat requirement was evaluated. • The synergistic effect was found for CO 2 absorption into DMEA/MEA solution. • A correlation was developed for the prediction of mass transfer coefficient (K G). Abstract Combination N,N -dimethylethanolamine(DMEA) and monoethanolamine (MEA) may represent a potential absorbent for CO 2 capture due to the high absorption rate, high cyclic CO 2 capacity and low energy requirement for solvent regeneration. Both the absorption and regeneration performances for 2 kmol/m3 DMEA/MEA with molar ratios of 2.0:0.0, 1.5:0.5, 1.0:1.0, 0.5:1.5, and 0.0:2.0 were estimated in terms of the absorption rate, regeneration rate and cyclic CO 2 capacity using an improved rapid screening method. The experimental results showed that the highest cyclic CO 2 capacities (i.e. low energy requirement) for the cyclic reaction time of 30 min and 60 min were obtained both by 1.0 M DMEA + 1.0 M MEA solution, indicating the synergistic effects existing in CO 2 absorption into DMEA/MEA solution. Additionally, the mass transfer performance of CO 2 absorption into 1.0 M DMEA + 1.0 M MEA solution was investigated in a hollow fiber membrane contactor. The effects of key operational parameters such as liquid velocity, inlet gas flow rate, CO 2 partial pressure, feed temperature range, CO 2 lean loading, amine concentration and membrane contactor height on the CO 2 flux and overall gas phase mass transfer coefficient were investigated. Furthermore, a developed correlation was successfully applied for the prediction of overall gas phase mass transfer coefficient (K G) for CO 2 absorption into DMEA/MEA solution, with an average absolute relative deviation (AARD) of 8.31%. Thus, a potential absorbent (i.e. DMEA/MEA) for CO 2 capture was proposed in this work. [ABSTRACT FROM AUTHOR]

Highlights • An inverse relationship between the mass transfer and permeability was found. • Mass transport processes are strongly influenced by microstructural anisotropy. • Mass transfer correlations were presented for media with varying anisotropy. Abstract A numerical method for calculating the mass transfer coefficient in fibrous media is presented. First, pressure driven flow was modelled using the Lattice Boltzmann Method. The advection-diffusion equation was solved for convective-reacting porous media flow, and the method is contrasted with experimental methods such as the limiting current diffusion technique, for its ability to determine and simulate mass transfer systems that are operating at low Reynolds number flows. A series of simulations were performed on three materials; specifically, commercially available carbon felts, electrospun carbon fibers and electrospun carbon fibers with anisotropy introduced to the microstructure. Simulations were performed in each principal direction (x,y,z) for each material in order to determine the effects of anisotropy on the mass transfer coefficient. In addition, the simulations spanned multiple Reynolds and Péclet numbers, to fully represent highly advective and highly diffusive systems. The resulting mass transfer coefficients were compared with values predicted by common correlations and a good agreement was found at high Reynolds numbers, but less so at lower Reynolds number typical of cell operation, reinforcing the utility of the numerical approach. Dimensionless mass transfer correlations were determined for each material and each direction in terms of the Sherwood number. These correlations were analyzed with respect to each materials' permeability tensor. It was found that as the permeability of the system increases, the expected mass transfer coefficient decreases. Two general mass transfer correlations are presented, one correlation for isotropic fibrous media and the other for through-plane flow in planar fibrous materials such as electrospun media and carbon paper. The correlations are Sh = 0.879 Re0.402 Sc0.390 and Sh = 0.906 Re0.432 Sc0.432 respectively. [ABSTRACT FROM AUTHOR]

Abstract The salt dissolution in aqueous drilling fluids is one of the main problems founded in well drilling of salt layers. The dissolution may cause the well enlargement, the salt layer outflow towards the drilling column or a drill immobilization resulted by the accumulation of saline gravels in the well bottom. In this study, the dissolution of sodium chloride (NaCl) particles and its influence on the physicochemical properties of fluids viscosified with bentonite were evaluated. In the rheological study of suspensions, the effect of time in the apparent viscosity was evaluated by the analysis of different bentonite and salt concentrations. The dissolved salt in the dispersion provided an apparent viscosity reduction and, regardless of the added salt mass, the shear stress values obtained were lower than those values in the pure bentonite dispersions. The dissolution kinetic was studied in a stirred tank, where experimental profiles of salt concentration in the liquid phase were obtained. The experimental data were used to evaluate the mass transfer coefficient in different conditions and to validate the mathematical model. The rate of salt particles dissolution was affected by both the fluid's bentonite and initial salt concentration. The mathematical model was used to simulate the process by the application of the mass conservation equations applied on both solid and fluid phase. The global mass transfer coefficients were estimated, and its values were in the range of 0.250 × 10−4 to 0.792 × 10−4 m/s. The experimental results were compared with those provided by the model with an error less than 10%. Graphical abstract Salt concentration predicted by the mathematical model and experimental salt concentration for dispersions with 10 lb/bbl of bentonite. Image 1 Highlights • Bentonite suspensions were used to study the dissolution kinetics of NaCl. • The dissolved salt provides a reduction in the apparent viscosity. • The fluid's bentonite and initial salt concentration affect the salt dissolution. • A model for dissolution kinetics of salt was applied in the experimental data. • Mass transfer coefficients were estimated. [ABSTRACT FROM AUTHOR]

Stirred tank reactors are most commonly used both in the laboratory and industry. Particularly for bioreactors, the volumetric mass transfer coefficient (kLa) of oxygen is used as one of the important parameters for determining efficiencies of reactors and for successful scale‐up. A number of correlation methods have been previously developed to predict the kLa in stirred tank bioreactors. In the present work, we propose a new correlation for kLa based on a mathematical and statistical approach using Response Surface Methodology (RSM) based on Box‐Behnken design of experiments. This correlation includes the effect of various parameters such as impeller agitation rate (50–800 rpm), air flow rate (0.5–3.5 L/min), and temperature (10−40°C) for different impeller configurations (single and dual Rushton, pitched blade, and mixed turbines). It was observed that the kLa increases with increasing the parameters for all the impeller configurations studied. Among the operating parameters, the most significant variable impacting kLa was found to be agitation rate, followed by air flow rate, and temperature. The models developed using RSM successfully interpreted the experimental kLa and were further validated under other operating conditions. It was also found that, compared with conventional power‐law models, the RSM approach enables a more efficient correlation procedure and formulates simplified models with comparably high accuracy, suggesting that the RSM is promising for evaluation of oxygen mass transfer in stirred tank bioreactors. © 2018 American Institute of Chemical Engineers Environ Prog, 38: 387–401, 2019 [ABSTRACT FROM AUTHOR]

Concentration polarization (CP) is mostly evaluated through one-dimensional (1D) film models considering convective and diffusive transport of solutes. However, in multicomponent ionic solutions, electromigration and chemical speciation may also play a role in the solute transport within the CP layer, thus affecting the process performance. We developed a three-dimensional (3D) numerical model for evaluating the CP in spacer-filled feed reverse osmosis (RO) channels by coupling hydrodynamics with the transport of solutes by convection, diffusion and electromigration, and chemical speciation by several ion-pairing equilibria. A realistic spacer geometry was obtained by CT-scans of commercial RO spacers. The model revealed highly non-uniform distributions of CP, mass transfer coefficients and precipitation potential on the membrane. While electromigration tends to equalize the fluxes of dominant ions, increases locally the CP of anions and decreases that of cations, it was found not to significantly affect the boundary layer thickness. However, the chemical speciation strongly affected the CP of trace ions binding with dominant ions. Finally, the 3D results were compared with those obtained from simpler 1D models. While 1D approaches help explaining qualitatively the effects of electromigration and speciation, and serve as a reasonable first approximation, they do not capture the non-uniform distribution of concentrations, mass transfer rates or saturation indices. The model will be used to study the full length of an RO membrane module and thus provide better indicators of the overall performance of the separation process. [Display omitted] • Hydrodynamics and mass transport with real 3D feed spacer geometry. • Concentration polarization model includes electromigration and chemical speciation. • Chemical speciation strongly influences the polarization and boundary layer thickness. • Non-uniform mass transfer coefficients and precipitation potential on the membrane. • 1D model results are only qualitatively comparable with those of the 3D model. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics simulations are used to model the velocity field and the transport of a passive scalar within a micro-scale chamber used to measure diffusional transport through various building materials. Comparisons of solutions obtained using a steady, laminar flow assumption with velocity measurements obtained from hot-wire anemometry show that the numerical method generally underpredicts the near surface velocity field. The results improve for higher flow rates and for carpeted test materials, modeled as a porous resistive layer. Calculations involving scalar transport within the upper chamber of the sampling device are performed for different flow rates and Schmidt numbers. The results are used to develop a model for the convective mass transfer coefficient, correlated as a function of the Reynolds and Schmidt numbers as well as the porosity of the carpet. This model is integrated into a steady-state mass transport model for predicting the diffusion of gaseous formaldehyde through various test materials. Predictions of diffusion and partition coefficients for vinyl flooring, gypsum wall board, and carpet are within the ranges of literature data. The results indicate that a perfectly mixed upper part of the sampling device is an adequate assumption. [Display omitted] • CFD models are used to model the velocity field within a micro diffusion chamber. • Solutions obtained are compared with experimental measurements. • A model for the convective mass transfer coefficient is developed. • The model is used to predict formaldehyde diffusion through various materials. [ABSTRACT FROM AUTHOR]

One of the essential techniques for eliminating metallurgical silicon impurities during a metallurgical process is slag refining. In the present investigation, BaO and ZnO were added to a binary slag system composed of CaO–SiO 2 in weight percentages that varied from 5 to 20 %, and the effects of various slag system compositions, Slag-Si mass ratios (slag-silicon ratios), and refining times on the content of metallurgical silicon impurities were investigated. The mass transfer coefficients β A l and β B for Al and B were 3.01 × 10 − 6 m · s − 1 , 6.80 × 10 − 7 m · s − 1 , respectively, and the apparent rate constants (k B , k Al) of Al and B obtained for the refining time were 3.84 × 10 − 4 s − 1 and 8.67 × 10 − 5 s − 1 , respectively, The experimental results show that in the slagging refining process, the loss rate of silicon increases slightly with the extension of the refining time and is much smaller than that of the blowing refining, so it can be considered to be a more superior method of removing impurities from industrial silicon. • This paper studies the removal of impurities in refined silicon through slag-making experiments with different slag system compositions, different slag-to-silicon ratios and refining times. • The kinetics of the oxidative removal of impurities Al and B in the slagging process was simulated, and k B , k Al and β Al and β B were obtained. It provides theoretical support for the removal of impurities Al from industrial silicon. • It provides a basis for optimizing and upgrading the experimental conditions for refining and purifying industrial silicon slagging. [ABSTRACT FROM AUTHOR]

An experimental and numerical study was conducted to investigate the process of potato slices drying. For simulating the moisture transfer in the samples and predict the dehydration curves, a two-dimensional finite element model was developed and programmed in Compaq Visual Fortran, version 6.5. The model solved the Fick’s second law for slab in a shrinkage system to calculate the unsteady two-dimensional moisture transmission in rectangular coordinates (x,y). Moisture diffusivity and moisture transfer coefficient were determined by minimizing the sum squares of residuals between experimental and numerical predicted data. Shrinkage kinetics of the potato slices during dehydration was determined experimentally and found to be a linear function of removed moisture. The determined parameters were used in the mathematical model. The predicted moisture content values were compared to the experimental data and the validation results demonstrated that the dynamic drying curves were predicted by the methodology very well.

The mass transfer rate between steel and slag determines the reaction rates of elements in a molten bath(especially the reaction rates of desulphurization and dephosphorization),and has direct impact on the distribution ratios of elements between steel and slag. In this article,Hangang 250 t converter was taken as the research object. Factors such as gas flow,lance position and bottom blowing location were taken into consideration to study the mass transfer ability of the convertor by a water model whose similarity ratio was 1:9. The results show that increasing the top-blowing intensity and the bottom-blowing intensity can greatly improve the distribution ratios of elements in the molten bath between steel and slag. The mass transfer coefficient between steel and slag decreases obviously with the drop of bottom-blowing air flow,thus a bottom-blowing air flow not lower than 0.06 m3·t-1·min-1 is suggested. The more the bottom-blowing holes are,the larger the mass transfer coefficient between steel and slag gets. A distribution plan of bottomblowing air flow is presented,which is superior to the equal distribution plan of air flow.

In this study, whole lemons were dried using a laboratory convective hot air dryer and the effects of drying temperature on dehydration behaviour and mass transfer characteristics of the lemons were investigated. The drying experiments were conducted using air temperatures of 50, 60 and 75 °C and air velocity of 1 m/s. It was observed that the drying temperature affected the drying time and the drying rate significantly. Drying rate represented no constant period and the entire dehydration process took place in the falling rate period. The usefulness of five mathematical models to simulate the drying kinetics was evaluated and Midilli and logarithmic models were found as the best models describing the drying curves. The effective moisture diffusivity values were obtained to be 1.15×10-10, 2.29×10-10, and 7.63×10-10 m2/s for the applied temperatures, respectively. The activation energy was also determined to be 71.32 kJ/mol. The convective mass transfer coefficient values were calculated by the analytical model and obtained to be 4.078×10-7, 1.023×10-7 and 4.346×10-8 m/s for drying temperatures of 75, 60 and 50 °C, respectively.

Microalgae cultivation has received growing importance because of its potential applications in CO2 bio‐fixation, wastewater treatment and biofuel production. In this regard, proper design of photobioreactors is crucial for large‐scale commercial applications. The hydrodynamics of a photobioreactor has great influence on the transfer of CO2 from gas phase to liquid phase. Considering the facts, the present research focused on studying the gas holdups and mass transfer from the gas to liquid phase in a tubular photobioreactor at various superficial liquid velocities ranging from 8.4 to 22.4 cm/s and superficial gas velocities ranging from 3.66 to 8.1 cm/s. It was found that the gas holdups were radially distributed. The highest gas holdups were observed at the center zone while the lowest holdups are found near the reactor wall. CO2 mass transfer coefficient in the photobioreactor was also estimated under different superficial liquid velocities (0.206, 0.355 and 0.485 cm/s) and gas velocities (0.67, 1.16 and 1.37 cm/s). The overall mass transfer coefficient was estimated by fitting the experimental data and comparing results with an unsteady state differential mole balance equation solved by Runge‐Kutta‐Gill method. Model predictions were comparable to experimental results.